Approximately one million febrile infants aged ≤60 days present annually to pediatric emergency departments (PEDs) in Europe and the United States. Although fewer than 5% are diagnosed with meningitis or bacteremia (invasive bacterial infections - IBIs), and 10-15% with urinary tract infections (UTIs), current guidelines recommend extensive diagnostic evaluations, hospitalization, and empirical treatment with broad-spectrum parenteral antibiotics. This approach may contribute to medical overuse, with implications for patient care, healthcare resource utilization, and environmental sustainability.

The Febrile Infants Swedish Study (FISS) is a prospective observational study conducted across 11 PEDs in Sweden. All febrile infants aged ≤60 days presenting to participating sites will be eligible. A new clinical guideline for the management of infants with fever without source (FWS) will be implemented in 7 PEDs, while 4 PEDs will continue with current standard practice and serve as a comparison group.

The study is expected to run for approximately two years and aims to recruit a minimum of 2,500 febrile infants

BACKGROUND

Each year, around one million febrile infants aged ≤60 days present to pediatric emergency departments (PEDs) in Europe and the United States. Previous studies report that 2-5% of these infants are diagnosed with meningitis or bacteremia (invasive bacterial infections - IBIs) and 10-15% with urinary tract infections (UTIs). Due to the potential severity of these infections, current guidelines recommend comprehensive diagnostic evaluations, hospitalization, and empirical treatment with broad-spectrum antibiotics. Consequently, an estimated 800,000 infants undergo these interventions annually without confirmed SBI.

These practices may have unintended consequences. Lumbar punctures can be painful, stressful, and time-consuming, with unsuccessful attempts linked to longer hospital stays. Early antibiotic exposure has been associated with increased risks of chronic conditions and reduced vaccine response and contributes to antimicrobial resistance. Hospitalization may lead to complications, disrupt breastfeeding, and impose financial and emotional burdens on families. Routine testing can result in overdiagnosis and medical overuse. Additionally, healthcare delivery has environmental implications, with each hospital bed-day generating significant waste and energy consumption.

Current guidelines rely on binary thresholds for biomarkers such as CRP and procalcitonin. They also lack consideration of clinical context, such as the infant's condition or fever characteristics, resulting in a uniform approach that may not suit individual cases.

There is a need for more individualized, evidence-based guidelines that integrate clinical and laboratory findings to support risk stratification and informed decision-making. Guidelines that reduce unnecessary interventions may improve care, optimize resource use, and lessen environmental impact.

The Febrile Infants Swedish Study (FISS) aims to evaluate a new clinical guideline.

PRIMARY AIM

To evaluate the new guideline for the management of infants aged ≤60 days and compare to current praxis.

SECONDARY AIMS

• To collect clinical data (height/duration of fever, gestational age, birth weight, clinical symptoms/signs, laboratory results, diagnoses) which will enable the improvement of the guideline and the development of a more individualized management guideline.
• To describe adherence to the new guideline and variation between the study sites in the management of febrile infants aged ≤60 days.

STUDY DESIGN

This will be a multicenter prospective observational study in 11 PEDs in Sweden. All febrile infants presented to the study PEDs will be considered as eligible for the study. The new guideline will be implemented as the PEDs standard management protocol for infants aged ≤60 days with FWS in 7 PEDs (Lund, Malmö, Helsingborg, Kristianstad, Ystad, Örebro, Sachsska-Stockholm). In 4 PEDs (Uppsala, Gothenburg, Jönköping, and Karolinska-Stockholm), the management of febrile infants aged ≤60 days will continue according to current praxis and these PEDs will participate in this study as a control group

STUDY POPULATION

All febrile infants aged ≤60 days brought to any of the study PEDs will be considered eligible for the study.

INCLUSION CRITERIA

1. Age ≤60 days.
2. Temperature ≥38.0 C measured either at home or at the PED.

DEFINITIONS

Fever Without a Source (FWS): Defined as a body temperature ≥38°C, measured either at home or in the pediatric emergency department (PED), without an identifiable focus of infection following medical history and physical examination.

Serious bacterial infection (SBI) is defined as a Urinary Tract Infection (UTI), bacteremia, or bacterial meningitis.

Urinary tract infection (UTI) is defined as urine dipstick positive for leukocyte esterase or nitrite and a urine culture with growth of (1) any amount of a single pathogen in samples obtained by suprapubic aspiration; (2) ≥10,000 colony- forming units (cfu)/ml of a single pathogen in samples obtained by a 'clean catch' method or catheterization.

Bacteremia is defined as growth of a bacterial pathogen in a blood culture. The presence of coagulase- negative staphylococci, Propionibacterium spp, Bacillus cereus spp, micrococci, alpha haemolytic streptococci and diphtheroids were considered contaminants, unless indicated otherwise because of clinical or laboratory parameters.

Bacterial meningitis is defined by the presence of a cerebrospinal fluid (CSF) culture or a CSF polymerase chain reaction (PCR) test positive for a bacterial pathogen. Cases with indirect clinical or laboratory indications of bacterial meningitis, such as elevated CSF cell count with positive blood culture and negative CSF culture/PCR, especially if antibiotics are given before the lumbar puncture, can be considered as bacterial meningitis,

Invasive bacterial infection (IBI) is defined as bacterial meningitis or bacteremia.

Delayed treated SBI will be regarded in infants with an SBI who did not receive broad-spectrum antibiotics at the initial management.

Inclusion Criteria:

• Temperature ≥38.0 C (measured either at home or at the pediatric emergency department)
• Age ≤60 days

All febrile infants aged ≤60 days brought to any of the study Pediatric Emergency Departments will be considered eligible for the study.

Anonymised datasets not containing any personal data will be available after publication upon request

Beginning 2 years and ending 4 years after the publication of results